We propose to further characterize the properties of several previously described basal ganglia-enriched protein phosphorylation systems and phosphoprotein substrates for cAMP-dependent protein kinase. We will study the physiological and pharmacological regulation of the state of phosphorylation of phosphoproteins in intact cellular systems derived from basal ganglia structures. These include brain slices, synaptosomes, and dissociated striatal neurons. Both single and multiple interacting first messenger candidates (e.g.,dopamine and glutamate) will be examined in these systems. We will also study the levels of identified phosphoproteins following different pharmacological treatments which interfere with synaptic transmission in the basal ganglia and limbic regions. Finally, using electrophysiological methods, we will evaluate the physiological role of various components of the protein phosphorylation systems in the basal ganglia by direct intracellular injections of purified protein kinases, protein phosphatases, and phosphoproteins into isolated striatal neurons. The results are expected to increase our understanding of the mechanisms of signal transduction involved in normal and pathological conditions in the basal ganglia and associated limbic regions.